<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        .box{
            width: 500px;
            height: 500px;
            border: 1px solid #000;
            display: flex;
            flex-direction:row;  
            justify-content:center;
            align-items: center;

        }
        /*.box div{
            flex: 1; 
        }*/
        .one{
            background-color: red;
            /*height: 100px;*/
            width: 100px;
            height: 100px;

             
        }
        /*.two{
            background-color: pink;
            /*height: 100px;*/
            /*flex: 2;*/

        }
        .san{
            background-color: yellow;
            /*height: 100px;*/
        }*/
    </style>
</head>
<body>
    <div class="box">
        <div class="one"></div>
        <div class="two"></div>
        <div class="san"></div>
    </div>
</body>
</html>